Apparent Solubility Product Research Articles

Chemical Interactions between Thorium(IV) and O2- in the FLiBe and FLiNaK Molten Salt Systems

The chemical interactions between thorium(IV) and O2- in the LiF-BeF2 (2 : 1 mol%) (FLiBe) and LiF-NaF-KF (46.5 : 11.5 : 42 mol%) (FLiNaK) molten salt systems were studied at 873 K. The precipitation-dissolution behavior of Th(IV) oxide/oxyfluoride species, as well as the speciation law of these species and their relationship with oxide concentration in fluoride melts, were clarified. The results showed that the interactions between Th(IV) and O2- in the FLiBe melt would only produce ThO2. The saturated solubility of ThO2 in the FLiBe melt was 0.057 mol/kg, and its corresponding apparent solubility product ( K s p ′ ) was 8.8 ± 0.1 × 10 − 4 mol3/kg3 and 8.6 ± 0.7 × 10 − 4 mol3/kg3 by dissolution and oxide titration methods, respectively. However, in the FLiNaK melt, the interactions between Th(IV) and O2- were more complex than that in FLiBe, and Th(IV) oxyfluoride species (i.e., Th2OF104- and ThOF2) were produced. Th2OF104- was initially formed with the ratio of r ≤ 0.5 ( r = O 2 − added / Th IV initial ), and the Th2OF104- was converted to ThOF2 precipitate when r > 0.5 . Therefore, the soluble Th2OF104- is the important intermediate between Th(IV), O2-, and ThOF2 precipitation. The difference in results of the FLiBe and FLiNaK melts was attributed to the difference of free F- content in the two systems. The present work provided important reference and fundamental data for understanding the nature of thorium fuel precipitation and how to control it in the molten fluoride media, which is of significant importance for the safe operation of molten salt reactor (MSR).

Solubility and precipitation investigations of UO2 in LiF–BeF2 molten salt

The solubility of UO2 in molten LiF–BeF2 (2:1 mol) (FLiBe) eutectic salt at 600 °C was studied by chemical and electrochemical methods. The results of dissolution experiment showed that the saturated solubility of UO2 in this melt was 2.37 × 10−3 mol/kg and its corresponding apparent solubility product (Ksp’) was approximately 1.67 × 10−5 mol3/kg3. When more Li2O were added to the FLiBe–UF4 system, the cathodic peak current of U(IV) in the electrochemical cyclic voltammetry (CV) curve accordingly decreased because of precipitate formation. The precipitate corresponded to UO2 as determined by stoichiometric ratio (concentration variation of U4+ and O2−) and X-ray diffraction (XRD) analysis. Compared to the chemical analysis method, the CV technique was confirmed to be more feasible for accurate determination of concentration of U(IV). Meanwhile, the Ksp’ value was also obtained to be 1.33 × 10−5 mol3/kg3 during the whole oxide titration procedure, which was highly consistent with that from the dissolution experiment. With the value of Ksp’, the allowable amount of dissolved oxide ions (oxide tolerance) can be theoretically estimated in the FLiBe–UF4 system.

Experimental determination of the solubility product of dolomite at 50–253 °C

The ‘dolomite problem’, the scarcity of present-day dolomite formation near the Earth’s surface, has attracted much attention over the past century. Solving this problem requires having reliable data on the stability and kinetics of formation of this mineral. Toward this goal, the solubility of natural dolomite (CaMg(CO3)2) has been measured from 50 to 253 °C in 0.1 mol/kg NaCl solutions using a hydrogen electrode concentration cell (HECC). The obtained apparent solubility products (Kapp-sp-dol), for the reaction: CaMg(CO3)2 = Ca2+ + Mg2+ + 2CO32−, were extrapolated to infinite dilution to generate the solubility product constants for this reaction (Ksp°-dol). The derived equilibrium constants were fit and can be accurately described by log10Ksp°-dol = a + b/T (K) + cT (K) where a = 17.502, b = −4220.119 and c = −0.0689. This equation and its first and second derivatives with respect to T were used together with corresponding aqueous species properties to calculate the revised standard state thermodynamic properties of dolomite at 25 °C and 1 bar, yielding a Gibbs energy of formation (ΔfG298.15∘) equal to −2160.9 ± 2 kJ/mol, (log10Ksp°-dol = −17.19 ± 0.3); an enthalpy of formation (ΔfH298.15∘) of −2323.1 ± 2 kJ/mol, an entropy (S298.15∘) of 156.9 ± 2 J/mol/K and heat capacity (Cp298.15∘) of 154.2 ± 2 J/mol/K (uncertainties are 3σ). The dolomite solubility product derived in this study is nearly identical to that computed using SUPCRT92 (Johnson et al., 1992) at 200 °C, but about one order of magnitude higher at 50 and 25 °C, suggesting that dolomite may be somewhat less stable than previously assumed at ambient temperatures.

A Novel Kinetic Method to Measure Apparent Solubility Product of Bulk Human Enamel.

Introduction: Tooth enamel mineral loss is influenced by its solubility product value, which is fundamental to the understanding of de- and remineralization resulting from a carious or erosive challenge. Published pKsp values for human enamel and hydroxyapatite range from 110 to 126 suggesting a heterogeneous nature of enamel solubility. However, this range of values may also result from the variety of methods used, e.g., some authors reporting values for suspensions of enamel powder and others for bulk enamel. The aim of this study was to develop a method to measure the solubility of bulk human enamel under controlled in vitro conditions simulating demineralization behavior of enamel within the oral environment using scanning microradiography (SMR). SMR was used to monitor real-time changes in enamel demineralization rates at increasing calcium concentrations in a caries simulating demineralization solution until the concentration at which thermodynamic equilibrium between enamel and solution was achieved.Method: 2 mm thick caries free erupted human enamel slabs with the natural buccal surfaces exposed were placed in SMR cells exposed to circulating caries-simulating 2.0 L 0.1 M pH = 4.0 acetic acid, at 25°C. SMR was used to continuously measure in real-time the decrease in mineral mass during the demineralization at 5 different points from on each slab. Demineralization rates were calculated from a linear regression curve of projected mineral mass against demineralization time. Changes in the demineralization rates were monitored following a series of successive increases in calcium (and phosphate at hydroxyapatite stoichiometric ratios of Ca:P 1.67) were added to the demineralizing solution, until demineralization ceased. The pH was maintained constant throughout.Results: Demineralization halted when the calcium concentration was ~30 mM. At higher calcium concentrations, mineral deposition (remineralization) occurred. By comparison with results from speciation software calculations for the calcium phosphate ternary system, this result suggests that the bulk solubility product of enamel (pKspBEnamel) under the conditions used is 121.Discussion: The apparent pKspBEnamel under these conditions was higher than many previous reported values, and much closer to those previously reported for HAp. However, this is a bulk value, and does not reflect that enamel is a heterogeneous material, nor the influence of ionic inclusions.

Selective Crystallization of Phosphoester Coordination Polymer for the Separation of Neodymium and Dysprosium: A Thermodynamic Approach.

Thermodynamics of the formation of coordination polymers (CPs) or metal-organic frameworks (MOFs) has not been focused on, whereas many CPs or MOFs have been synthesized in a solution. With a view of separating Nd3+ and Dy3+ in an aqueous solution, we demonstrate that crystallization of the CPs of Nd3+ and Dy3+ based on dibutyl phosphoric acid (Hdbp) can be thermodynamically described; crystallization yields of [Ln(dbp)3] (Ln = Nd or Dy) complex are predicted well using a simple calculation, which takes the apparent solubility products (Kspa) for [Ln(dbp)3] and the acid dissociation constant of Hdbp into account. The Kspa values of [Nd(dbp)3] and [Dy(dbp)3] are experimentally determined to be (1.3 ± 0.1) × 10-14 and (2.9 ± 0.4) × 10-18 M4, respectively, at 20 °C. The ratio of these Kspa values, that is, ca. 4500, is significantly larger than the ratio of the solubility products for inorganic salts of Nd3+ and Dy3+. Therefore, Nd3+ and Dy3+ are selectively crystallized in an aqueous solution via the formation of CPs. Under optimized conditions, Dy3+ crystallization is preferable, whereas Nd3+ remains in the solution phase, where the ratio of the Dy molar content to the total metal content (i.e., Nd + Dy) in the crystal is higher than 0.9. The use of acids, such as HCl or HNO3, has no practical impact on the separation in an aqueous solution.

Electrochemical technique for detecting the formation of uranium-containing precipitates in molten fluorides

The electrochemical behavior of U(IV) in molten LiF–NaF–KF (46.5:11.5:42mol) (FLINAK) eutectic salt was studied by cyclic voltammetry and square-wave voltammetry analyses. The reduction of U(IV) proceeded in two steps: reduction of initial U(IV) to U(III), followed by three-electron reduction of U(III) to U metal. Both reactions were reversible and controlled by ion diffusion at a scan rate of 0.02–0.3Vs−1. A linear relationship between the reduction current density of U(III)/U(0) and the concentration of U(IV) was also established within 0.01–0.084molkg−1. When different concentrations of Li2O were added to the FLINAK–UF4 system, the peak current density of U(III)/U(0) was depleted because of the formation of UO2 precipitates. The apparent solubility product (Ksp) of UO2 in FLINAK–UF4–Li2O melts was approximately 4.75×10−6 mol3/kg3, which can be used to evaluate the allowable amount of dissolved oxide ions in uranium-based fluorides.

Climatological distribution of aragonite saturation state in the global oceans

AbstractAragonite saturation state (Ωarag) in surface and subsurface waters of the global oceans was calculated from up‐to‐date (through the year of 2012) ocean station dissolved inorganic carbon (DIC) and total alkalinity (TA) data. Surface Ωarag in the open ocean was always supersaturated (Ω > 1), ranging between 1.1 and 4.2. It was above 2.0 (2.0–4.2) between 40°N and 40°S but decreased toward higher latitude to below 1.5 in polar areas. The influences of water temperature on the TA/DIC ratio, combined with the temperature effects on inorganic carbon equilibrium and apparent solubility product (K′sp), explain the latitudinal differences in surface Ωarag. Vertically, Ωarag was highest in the surface mixed layer. Higher hydrostatic pressure, lower water temperature, and more CO2 buildup from biological activity in the absence of air‐sea gas exchange helped maintain lower Ωarag in the deep ocean. Below the thermocline, aerobic decomposition of organic matter along the pathway of global thermohaline circulation played an important role in controlling Ωarag distributions. Seasonally, surface Ωarag above 30° latitudes was about 0.06 to 0.55 higher during warmer months than during colder months in the open‐ocean waters of both hemispheres. Decadal changes of Ωarag in the Atlantic and Pacific Oceans showed that Ωarag in waters shallower than 100 m depth decreased by 0.10 ± 0.09 (−0.40 ± 0.37% yr−1) on average from the decade spanning 1989–1998 to the decade spanning 1998–2010.

Zinc solubility and fractionation in cultivated calcareous soils irrigated with wastewater

The solubility, lability and fractionation of zinc in a range of calcareous soils from Peshawar, Pakistan were studied (18 topsoils and 18 subsoils). The lability (E-value) of Zn was assessed as the fraction isotopically exchangeable with 70Zn2+; comparative extractions included 0.005M DTPA, 0.43M HNO3 and a Tessier-style sequential extraction procedure (SEP). Because of the extremely low concentration of labile Zn the E-value was determined in soils suspended in 0.0001M Na2-EDTA which provided reliable analytical conditions in which approximately 20% of the labile Zn was dissolved. On average, only 2.4% of soil Zn was isotopically exchangeable. This corresponded closely to Zn solubilised by extraction with 0.005 DTPA and by the carbonate extraction step (F1+F2) of the Tessier-style SEP. Crucially, although the majority of the soil CaCO3 was dissolved in F2 of the SEP, the DTPA dissolved only a very small proportion of the soil CaCO3. This suggests a superficial carbonate-bound form of labile Zn, accessible to extraction with DTPA and to isotopic exchange. Zinc solubility from soil suspended in 0.01M Ca(NO3)2 (PCO2 controlled at 0.03) was measured over three days. Following solution speciation using WHAM(VII) two simple solubility models were parameterised: a pH dependent ‘adsorption’ model based on the labile (isotopically exchangeable) Zn distribution coefficient (Kd) and an apparent solubility product (Ks) for ZnCO3. The distribution coefficient showed no pH-dependence and the solubility model provided the best fit to the free ion activity (Zn2+) data, although the apparent value of log10 Ks (5.1) was 2.8log units lower than that of the mineral smithsonite (ZnCO3).

The apparent solubility of aluminum (III) in Hanford high-level waste

The solubility of aluminum in Hanford nuclear waste impacts on the processability of the waste by a number of proposed treatment options. For many years, Hanford staff has anecdotally noted that aluminum appears to be considerably more soluble in Hanford waste than the simpler electrolyte solutions used as analogues. There has been minimal scientific study to confirm these anecdotal observations, however. The present study determines the apparent solubility product for gibbsite in 50 tank samples. The ratio of hydroxide to aluminum in the liquid phase for the samples is calculated and plotted as a function of total sodium molarity. Total sodium molarity is used as a surrogate for ionic strength, because the relative ratios of mono-, di- and trivalent anions are not available for all of the samples. These results were compared to the simple NaOH-NaAl(OH)4-H2O system, and the NaOH-NaAl(OH)4-NaCl-H2O system data retrieved from the literature. The results show that gibbsite is apparently more soluble in the samples than in the simple systems whenever the sodium molarity is greater than 2M. This apparent enhanced solubility cannot be explained solely by differences in ionic strength. The change in solubility with ionic strength in simple systems is small compared to the difference between aluminum solubility in Hanford waste and the simple systems. The reason for the apparent enhanced solubility is unknown, but could include kinetic or thermodynamic factors that are not present in the simple electrolyte systems. Any kinetic explanation would have to explain why the samples are always supersaturated whenever the sodium molarity is above 2M. Real waste characterization data should not be used to validate thermodynamic solubility models until it can be confirmed that the apparent enhanced gibbsite solubility is a thermodynamic effect and not a kinetic effect.

In Vitro Assessment of the Formation of Ceftriaxone–Calcium Precipitates in Human Plasma

Ceftriaxone is a third-generation cephalosporin antibiotic, which has a broad spectrum of bactericidal activity. Ceftriaxone is highly soluble as a sodium salt, but far less soluble as a calcium salt. Incompatibility of ceftriaxone with calcium and the possible formation of precipitates have been stated in the product label from early on. It was the objective of the present in vitro study to further assess the risk of precipitation of calcium-ceftriaxone in human plasma. Analytical methods were developed (high-performance liquid chromatography and flame atomic absorption spectroscopy) to quantitate calcium and ceftriaxone in human plasma supernatants and human plasma precipitates. Using high concentrations of ceftriaxone (10 mmol/L) and calcium (4.2 mmol/L) did not result in any precipitation after 2 h incubation in human plasma at 37 °C. Under conditions of forced precipitation only, formation of precipitation was observed. The identity of the precipitated material was confirmed by energy-dispersive X-ray analysis and Fourier transform infrared spectroscopy. We conclude that calcium-ceftriaxone in human plasma has an apparent kinetic solubility product constant of greater than 0.42 × 10(-4) (mol/L)(2), which exceeds the normal thermodynamic solubility product in water by a factor of 26. Under these conditions, the formation of plasma precipitates is unlikely.

Experimental determination of the solubility product of magnesite at 50 to 200 °C

Accurate knowledge of magnesite thermodynamic properties over a wide range of temperatures is crucial for characterizing mineral stabilities in the system MgO–CO 2–H 2O and for modeling carbon dioxide fate in important natural and industrial processes. However, available databases, especially for its solubility product, are sparse and contradictory, leading to considerable uncertainties in the calculation of chemical equilibria and phase transformations among carbonates. In this study, the solubility of synthetic magnesite was investigated from 50 to 200 °C in 0.1 mol kg − 1 NaCl solutions and in some cases under constant CO 2 partial pressure (4–30 bars) both by means of a hydrogen electrode concentration cell (HECC) and a traditional batch Ti-reactor. The obtained apparent solubility products ( Q sp-mgs) were extrapolated to infinite dilution to generate the solubility products ( K sp°-mgs), allowing calculation of the thermodynamic properties of magnesite. Of all the temperature functions tested, the equation giving a reliable fit of our data in the investigated temperature range (50–200 °C) has the following form: log 10 K sp°-mgs = a + b / T (K) + cT (K) with: a = 7.267, b = − 1476.604 and c = − 0.033918. Based on this equation and its first and second derivatives with respect to T, we were able to derive values at 25 °C, 1 bar for magnesite thermodynamic functions: Δ f G 298.15 o = (− 1026.48 ± 2) kJ mol − 1 (log 10 K sp°-mgs = − 7.80 ± 0.3), Δ f H 298.15 o = (− 1111.75 ± 2) kJ mol − 1 , S 298.15 o = (60.00 ± 2) J mol − 1 K − 1 , and C p 298.15 o = (75.91 ± 2) J mol − 1 K − 1 (uncertainties are 3 σ).

Common ion effect on solubility and dissolution rate of the sodium salt of an organic acid

The solubility and the dissolution rate of the sodium salt of an acidic drug (REV 3164; 7-chloro-5-propyl-1H,4H-[1,2,4]triazolo[4,3-alpha]quinoxaline-1,4-dione) decreased by the effect of common ion present in aqueous media. The solubility of the sodium salt of REV 3164 in a buffered medium was much lower than that in an unbuffered medium. Also, the presence of NaCl decreased its solubility in water. The apparent solubility product (K'sp) of the salt, however, did not remain constant when the concentration of NaCl was changed. A decrease in K'sp value with the increase in NaCl concentration was observed; for example, the K'sp values at 0 and 1 M NaCl were 7.84 X 10(-4) and 3.94 X 10(-4) M2, respectively. Even when corrected for the effect of ionic strength, the solubility product decreased. This decrease in the solubility product in the presence of NaCl indicated a decrease in the degree of self-association (increase in activity coefficient) of the drug in aqueous media.

Modelling ion composition in simulated milk ultrafiltrate (SMUF). I: Influence of calcium phosphate precipitation

Freshly prepared simulated milk ultrafiltrate (SMUF) is a solution that is supersaturated with respect to various calcium phosphate phases that precipitate in time. As a consequence, the ion composition of equilibrated SMUF was found to be significantly different from that of freshly prepared SMUF. This study proposes a thermodynamic ion-speciation model that is able to describe ion equilibria in SMUF. Moreover, it is also able to describe calcium phosphate precipitation in fresh SMUF on its way to equilibrium by using an apparent solubility product for CaHPO 4·2H 2O as a function of time. The model was validated by experiments in which CaCl 2 and Na 2HPO 4 were added to freshly prepared SMUF. The changes in calcium activity and pH were followed and the precipitates were characterised by X-ray diffraction. The model was able to predict the observed changes.

Monitoring ZnS Precipitation: Estimation, Error Analysis and Experiment Design

A mass balance model of total soluble sulfide and free zinc with a second-order reaction term is theoretically able to reconstruct the zinc effluent concentration and the kinetic parameter (k). However, under real conditions this model predicts the zinc effluent concentration four orders of magnitude higher than the measured ones. The applied error analysis, based on linearization of the model followed by first-order variance propagation, showed that the accuracy of several of the input variables (flows and influent concentrations) jeopardized the estimation of the Zn concentration in the effluent, which is a phenomenon expected for every fast reaction with low product concentration. In order to overcome the inaccuracy issue, an “apparent solubility product” as a function of pS (11-20) was calculated from the experimental data, allowing for the subsequent determination of an “apparent kinetic parameter” (k A ), that excluding parallel reactions was between 1.7 × 1023 – 6.2 × 1024 L/(mol·h). This allowed for further tuning of the model such that the estimates of the Zn effluent concentration became of the same order of magnitude as the measured ones (10−7 M Zn).

Initial Salt Screening Procedures for Manufacturing Ibuprofen

The aim of this paper is to design initial salt screening procedures for manufacturing ibuprofen. Salt forms of a pharmaceutical acid racemic (R,S)-(±)-ibuprofen and their “developable” synthetic routes were ferreted out simultaneously through the screening of seven bases of sodium hydroxide, potassium hydroxide, l-arginine, l-histidine, l-lysine, diethanolamine, and tris(hydroxymethyl)aminomethane (THAM), and the match with the use of nine organic solvents of methanol, dimethyl sulfoxide, ethanol, N, N-dimethylformamide, acetonitrile, isopropyl alcohol, 1,4-dioxane, acetone, and tetrahydrofuran mainly in the presence of water in 20 mL scintillation vials. Racemic (R,S)-(±)-sodium ibuprofen dihydrate, a well-known ibuprofen salt and the newly discovered racemic (R,S)-(±)-THAM ibuprofen, appeared as white-squared powders with a molecular weight of 327.42 g/mol, a melting point of 160.17°C, and the apparent solubility product, K′sp, of 6.0 × 10−4 M2 at 25°C were successfully synthesized by the initial salt screening methods. The new amine salt of ibuprofen was monoclinic and had a space group of P21/c and lattice parameters of a = 17.578(8)°, b = 10.428(4)°, c = 9.991(4) Å, α = 90.00°, β = 97.17(1)°, γ = 90.00°, and V = 1,817.05(244) Å3. The aspect ratio of the amine salt crystals of ibuprofen of ≈ 1.0 implied that the crystals had a better flowability than the sodium salt counterparts. This amine salt of ibuprofen was more stable in moist or dried atmospheres and was more hydrophobic than the sodium salt of ibuprofen. Moreover, the slow dissolution of this amine salt of ibuprofen might have made it less bitter and more suitable as a sustained release drug than the sodium salt of ibuprofen. The future work is to search for the different polymorphs of this amine salt of ibuprofen and to extend the initial salt screening working logics to the formation of co-crystals.

Solubility product of siderite (FeCO 3) as a function of temperature (25–250 °C)

The solubility of natural siderite was investigated from 25 to 250 °C in 0.1 mol kg − 1 NaCl aqueous solutions using a hydrogen-electrode concentration cell, which provided continuous in situ measurement of hydrogen ion molality. Iron(II) was analyzed by a revised Ferrozine-spectrophotometric method. The obtained apparent solubility products ( Q sp-siderite) were extrapolated to infinite dilution to generate the solubility products ( K sp°-siderite), allowing calculation of the thermodynamic properties of siderite. Of all the temperature functions tested, the equation giving a reliable fit of our data in the investigated temperature range (25–250 °C) has the following form: log 10 K sp°-siderite = a + b ∙ ( T / K ) + c ∙ ( T / K) − 1 + d ∙ log 10 (T / K) with: a = 175.568, b = 0.0139, c = − 6738.483 and d = − 67.898. Based on this equation and its first and second derivatives with respect to T, we were able to derive values for the Gibbs energy of formation: Δ fG 298.15 o = (− 680.71 ± 2) kJ mol − 1, enthalpy of formation: Δ fH 298.15 o = (− 749.59 ± 2) kJ mol − 1, entropy: S 298.15 o = (109.54 ± 2) J mol − 1 K − 1 and heat capacity: C p 298.15 o = (83.26 ± 2) J mol − 1 K − 1 of siderite (uncertainties are 3 σ). The values of Δ fG 298.15 o and Δ fH 298.15 o are in very good agreement with the values reported by Robie et al. [Robie, R.A., Haselton, H.T. Jr., Hemingway, B.S., 1984. Heat capacities and entropies of rhodochrosite (MnCO 3) and siderite (FeCO 3) between 5 and 600 K. Am. Mineral. 69, 349–357] and Chai and Navrotsky [Chai, L., Navrotsky, A., 1994. Enthalpy of formation of siderite and its application in phase equilibrium calculation. Am. Mineral. 79, 921–929], respectively. The density model [Anderson, G.M., Castet, S., Schott, J., Mesmer, R.E., 1991. The density model for estimation of thermodynamic parameters of reactions at high temperatures and pressures. Geochim. Cosmochim. Acta 55, 1769–1779] reproduced correctly our experimental data and allowed the extrapolation of the siderite solubility product up to 350 °C by using our values of the Gibbs energy and enthalpy of formation of siderite combined with its entropy and the heat capacity equation given by Robie et al. [Robie, R.A., Haselton, H.T. Jr., Hemingway, B.S., 1984. Heat capacities and entropies of rhodochrosite (MnCO3) and siderite (FeCO3) between 5 and 600 K. Am. Mineral. 69, 349–357].

Solubility of plutonium(VI) carbonate in saline solutions

Among the plutonium oxidation states found to form in the environment, mobile plutonium(VI) can exist under oxidizing conditions and in waters with high chloride content due to radiolysis effects. We are investigating the solubility and speciation of plutonium(VI) carbonate under conditions relevant to natural waters and brines such as those found near some geologic radioactive waste repositories. The solid Pu(VI) phase PuO 2CO 3(s) was prepared and its solubility was measured in NaCl and NaClO 4 solutions in a CO 2 atmosphere as a function of pH and ionic strength (0.1–5.6 m). The concentration of soluble plutonium in solution was calculated from spectroscopic data and liquid scintillation counting. Spectroscopic measurements also revealed the plutonium oxidation state. The apparent solubility product of PuO 2CO 3(s) was determined at selected electrolyte concentrations to be, log K s,0 = −13.95 ± 0.07 (0.1 m NaCl), log K s,0 = −14.07 ± 0.13 (5.6 m NaCl), and log K s,0 = −15.26 ± 0.11 (5.6 m NaClO 4). Specific ion interaction theory was used to calculate the solubility product at zero ionic strength, log K s, 0 ∘ = − 14.82 ± 0.05 .

Boron Removal via Formation of Magnesium Silicate Solids during Precipitative Softening

Precipitative softening is an option to remove silicon and boron from natural waters. Silicon was removed from hard waters by precipitative softening when the molar ratio of Mg:Si was less than 6:1 by the formation of an amorphous magnesium silicate. This solid had an apparent solubility product constant of 10 -25.66 and was stoichiometrically similar to the mineral forsterite, Mg 2 SiO 4 . Boron removal was consistent with sorption to this amorphous magnesium silicate and could be roughly described by a Freundlich isotherm: B sorb /Mg 2 SiO 4(s) =21×B 0.51 sol .

Effect of Calcium and Magnesium Ions on Calcium Oxalate Formation in Sugar Solutions

During the concentration of sugarcane juice, there is continuous deposition of nonsugar impurities on the surface of evaporator units. Because the scale deposit has a low thermal conductivity, its accumulation impairs heat transfer and eventually renders the process uneconomical owing to reduced throughput. Calcium oxalate is the main intractable scale formed in factories that process sugarcane. It is not removed by conventional chemical cleaning methods. This paper describes studies on the apparent solubility product of calcium oxalate in the presence of sugar and calcium and magnesium ions at different temperatures and pH's. A solubility product model was obtained that states that the apparent solubility product of calcium oxalate decreases with increasing temperature and sugar concentration, but increases with increasing pH. The model was able to predict calcium oxalate solubility changes in raw sugarcane factory processes, indicating that the apparent solubility product of calcium oxalate declines rapidly through the evaporator set. The results also indicated that calcium oxalate solubility is increased in the presence of calcium and, in particular, magnesium ions.

Énergies d'hydratation et stabilité thermodynamique des minéraux argileux. I. Cas d'une argile fictive moyenne

By averaging a large number of experimental dehydration isotherm properties of various dioctahedral (Al 3+ , Fe 3+ ) or trioctahedral (Mg 2+ , Fe 2+ ) smectites (low interlayer charges) and vermiculites (high interlayer charges) saturated by Li + , Na + , K + , Mg 2+ or Ca 2+ , one may define a fictitious interstratified solid solution of hydrated layers. As an example of thermodynamic treatment, have been calculated as a function of water activity: water content, hydration energy, Gibbs free energies of formation, true and apparent solubility products. À partir d'un grand nombre d'isothermes d'hydratation obtenues expérimentalement sur des argiles dioctaédriques (Al 3+ , Fe 3+ ), trioctaédriques (Mg 2+ , Fe 2+ ), faiblement (smectites) ou fortement chargées (vermiculites) saturées par Li + , Na + , K + , Mg 2+ ou Ca 2+ , on a défini une argile de composition moyenne, sorte d'interstratifié fictif, solution solide de feuillets hydratés. À titre d'exemple du traitement thermodynamique, ont été calculés, en fonction des variations de l'activité de l'eau, la teneur en eau, l'énergie d'hydratation ainsi que les produits de solubilité vrais et apparents.